1. Field of the Invention
The present invention relates to a fluid compressor for compressing a refrigerant gas, which compressor is provided, for example, in a refrigerator.
2. Description of the Related Art
Conventionally, various types of compressors for compressing a refrigerant, for use in refrigerators, are known; for example, a reciprocal type compressor, a rotary type compressor, etc.
In these conventional compressors, structures of compressing units or driving units for driving crank shafts for transmitting torque to the compressing units are complex, and the number of parts is large.
In such a compressor, a check valve must be provided on the exhaust side in order to raise the compression efficiency. The difference in pressure between both sides of the check valve is very high. Thus, gas may leak from the check valve, and consequently the compression efficiency is low.
In order to achieve the above object, it is necessary to enhance the precision in dimensions of parts and the precision in assembly, resulting in an increase in manufacturing costs.
U.S. Pat. No. 4,871,304 discloses a fluid compressor wherein a rod is arranged eccentrically in the inside of a cylinder, a spiral groove is formed in an outer peripheral portion of the rod, and a spiral blade is slidably fitted in the groove such that the blade can freely enter and retreat from the groove.
The pitch of the blade decreases towards the discharge side of the fluid compressor. A high pressure is applied through a pressure introducing passage to the bottom space of the spiral groove in which the blade is fitted.
U.S. Pat. No. 4,872,820 discloses a fluid compressor having basically the same structure as the compressor of U.S. Pat. No. 4,871,304, wherein a spiral blade is inclined such that an outer peripheral portion of the blade faces the exhaust side.
U.S. Pat. No. 4,875,842 discloses a fluid compressor having basically the same structure as the compressor of U.S. Pat. No. 4,872,820, wherein one of bearings for supporting both ends of a cylinder and a rotor (piston) is supported so as to be movable in parallel to the axis of the cylinder and in the radial direction of the cylinder, but not to be rotatable.
In each of the above compressors, a compressed fluid is discharged into a sealed casing through a discharge passage formed in a bearing.
The compressed fluid filled in the sealed casing is exhausted through an exhaust pipe connected to the sealed casing. In the case where the exhaust pipe is connected to a refrigerator, the fluid is led to a condenser.
In the meantime, the compressed fluid discharged into the sealed casing through the discharge passage is mixed with lubricating oil which has been supplied to sliding portions for lubrication.
Since the lubricating oil is mixed in the compressed fluid, the lubricating oil is dispersed when it is discharged into the sealed casing.
The dispersed lubricating oil reaches the inner peripheral wall of the sealed casing, a motor unit, and the opening of the exhaust pipe connected to the sealed casing.
In particular, the lubricating oil dispersed at the opening of the exhaust pipe is exhausted to the outside of the sealed casing along with the compressed fluid Once the lubricating oil has been exhausted from the compressor, the lubricating oil does not easily return to the compressor.
In addition, if the lubricating oil is dispersed on the inner peripheral wall of the sealed casing and if part of the oil flows along the inner peripheral wall down to the vicinity of the opening of the exhaust pipe, the part of the oil may be sucked into the opening by the influence of the high-pressure compressed fluid within the sealed casing.
If this undesirable condition continues for a long time period, the quantity of the lubricating oil remaining in the sealed casing reduces and the quantity of oil to be supplied to sliding portions runs short, resulting in lack of smoothness.